AD 2018-02-04 Aerospace Welding Inc

FAA SUMMARY: We are adopting a new airworthiness directive (AD) for certain Aerospace Welding Minneapolis, Inc. mufflers, part numbers A1754001-23 and A1754001-25, installed on airplanes. This AD was prompted by occurrences of cracks or broken welds in the connecting weld of the muffler body to muffler cuff that may allow carbon monoxide exhaust fumes into the cockpit heating system. This AD requires an inspection of the muffler for leaking to identify cracks and replacement of the muffler. We are issuing this AD to address the unsafe condition on these products.